Cellular systems are expected to evolve from today's 4G (LTE, 802.16m) to 5G which promise even larger data rates (up to 100 times greater). One of the candidates for 5G system is the use of millimeter wave bands in place of current PCS microwave bands used in 4G systems. The millimeter wave frequencies are an order of magnitude greater than today's PCS bands.
The nature of propagation is different in millimeter wave bands in that the propagation loss in free space is much larger than what is observed in the microwave bands. Given the shorter wavelength, the size of the antenna required to transmit millimeter waves is much smaller compared to those required for microwave bands. However, the smaller antennae can be packed in an area comparable to the antenna area for a microwave band. When this antenna array is “operated” synchronously, they form a beam whose gain can make up for the higher propagation loss.
In beamformed systems, a links from a mobile station to a base station use uplink channel sounding for sensing channel quality of transmissions to enable and enhance connections between the mobile station and the base station. Adding the use of multiple beams for both the mobile station and the base station increases complexity of uplink channel sounding.